全文获取类型
收费全文 | 3265篇 |
免费 | 269篇 |
国内免费 | 2篇 |
出版年
2023年 | 17篇 |
2022年 | 13篇 |
2021年 | 53篇 |
2020年 | 38篇 |
2019年 | 41篇 |
2018年 | 51篇 |
2017年 | 48篇 |
2016年 | 87篇 |
2015年 | 146篇 |
2014年 | 163篇 |
2013年 | 217篇 |
2012年 | 248篇 |
2011年 | 264篇 |
2010年 | 182篇 |
2009年 | 177篇 |
2008年 | 242篇 |
2007年 | 232篇 |
2006年 | 200篇 |
2005年 | 199篇 |
2004年 | 205篇 |
2003年 | 167篇 |
2002年 | 178篇 |
2001年 | 53篇 |
2000年 | 31篇 |
1999年 | 33篇 |
1998年 | 33篇 |
1997年 | 26篇 |
1996年 | 17篇 |
1995年 | 23篇 |
1994年 | 11篇 |
1993年 | 14篇 |
1992年 | 7篇 |
1991年 | 10篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 9篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 11篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1973年 | 3篇 |
1935年 | 1篇 |
排序方式: 共有3536条查询结果,搜索用时 15 毫秒
81.
Simon M. Smart Susan G. Jarvis Toshie Mizunuma Cristina Herrero‐Juregui Zhou Fang Adam Butler Jamie Alison Mike Wilson Robert H. Marrs 《Ecology and evolution》2019,9(22):12858-12868
Quantitative models play an increasing role in exploring the impact of global change on biodiversity. To win credibility and trust, they need validating. We show how expert knowledge can be used to assess a large number of empirical species niche models constructed for the British vascular plant and bryophyte flora. Key outcomes were (a) scored assessments of each modeled species and niche axis combination, (b) guidance on models needing further development, (c) exploration of the trade‐off between presenting more complex model summaries, which could lead to more thorough validation, versus the longer time these take to evaluate, (d) quantification of the internal consistency of expert opinion based on comparison of assessment scores made on a random subset of models evaluated by both experts. Overall, the experts assessed 39% of species and niche axis combinations to be “poor” and 61% to show a degree of reliability split between “moderate” (30%), “good” (25%), and “excellent” (6%). The two experts agreed in only 43% of cases, reaching greater consensus about poorer models and disagreeing most about models rated as better by either expert. This low agreement rate suggests that a greater number of experts is required to produce reliable assessments and to more fully understand the reasons underlying lack of consensus. While area under curve (AUC) statistics showed generally very good ability of the models to predict random hold‐out samples of the data, there was no correspondence between these and the scores given by the experts and no apparent correlation between AUC and species prevalence. Crowd‐sourcing further assessments by allowing web‐based access to model fits is an obvious next step. To this end, we developed an online application for inspecting and evaluating the fit of each niche surface to its training data. 相似文献
82.
Koen A. J. Pelsma Michiel H. in 't Zandt Huub J. M. Op den Camp Mike S. M. Jetten Joshua F. Dean Cornelia U. Welte 《Environmental microbiology》2022,24(1):82-97
Urbanised environments have been identified as hotspots of anthropogenic methane emissions. Especially urban aquatic ecosystems are increasingly recognised as important sources of methane. However, the microbiology behind these emissions remains unexplored. Here, we applied microcosm incubations and molecular analyses to investigate the methane-cycling community of the Amsterdam canal system in the Netherlands. The sediment methanogenic communities were dominated by Methanoregulaceae and Methanosaetaceae, with co-occurring methanotrophic Methanoperedenaceae and Methylomirabilaceae indicating the potential for anaerobic methane oxidation. Methane was readily produced after substrate amendment, suggesting an active but substrate-limited methanogenic community. Bacterial 16S rRNA gene amplicon sequencing of the sediment revealed a high relative abundance of Thermodesulfovibrionia. Canal wall biofilms showed the highest initial methanotrophic potential under oxic conditions compared to the sediment. During prolonged incubations the maximum methanotrophic rate increased to 8.08 mmol gDW−1 d−1 that was concomitant with an enrichment of Methylomonadaceae bacteria. Metagenomic analysis of the canal wall biofilm lead to the recovery of a single methanotroph metagenome-assembled genome. Taxonomic analysis showed that this methanotroph belongs to the genus Methyloglobulus. Our results underline the importance of previously unidentified and specialised environmental niches at the nexus of the natural and human-impacted carbon cycle. 相似文献
83.
Biodiversity and Conservation - Invasive predators, land clearing and altered fire regimes have been implicated in species decline and extinction worldwide. Enhanced knowledge of how these factors... 相似文献
84.
Xing Fu Mei-Jun Zhu Mike V. Dodson Min Du 《The Journal of biological chemistry》2015,290(44):26445-26456
Satellite cells are the major myogenic stem cells residing inside skeletal muscle and are indispensable for muscle regeneration. Satellite cells remain largely quiescent but are rapidly activated in response to muscle injury, and the derived myogenic cells then fuse to repair damaged muscle fibers or form new muscle fibers. However, mechanisms eliciting metabolic activation, an inseparable step for satellite cell activation following muscle injury, have not been defined. We found that a noncanonical Sonic Hedgehog (Shh) pathway is rapidly activated in response to muscle injury, which activates AMPK and induces a Warburg-like glycolysis in satellite cells. AMPKα1 is the dominant AMPKα isoform expressed in satellite cells, and AMPKα1 deficiency in satellite cells impairs their activation and myogenic differentiation during muscle regeneration. Drugs activating noncanonical Shh promote proliferation of satellite cells, which is abolished because of satellite cell-specific AMPKα1 knock-out. Taken together, AMPKα1 is a critical mediator linking noncanonical Shh pathway to Warburg-like glycolysis in satellite cells, which is required for satellite activation and muscle regeneration. 相似文献
85.
Systematic assessment of the Atelostomata (Spatangoida and Holasteroida; irregular echinoids) based on spine microstructure 下载免费PDF全文
Spines of irregular echinoids occur in very high abundance in each specimen, and display distinct architecture as a result of the specialized functions of the spines; however, studies on spine microstructure in atelostomate echinoids have rarely been carried out. Accordingly, little is known about their specific morphology. This work aims to elaborate differences in the spine morphology of selected Atelostomata (Spatangoida and Holasteroida) in detail, and to discuss spine microstructure for its potential systematic value. Based on 82 atelostomate species (56 spatangoids and 26 holasteroids), we show that the perforation pattern in the internal cylinder of the spine (helicoidal versus horizontal pattern) provides a safe distinction between the Spatangoida and Holasteroida. According to this character we discuss the geological history of atelostomate echinoids, in particular their migration into the deep sea, based on well‐preserved records of fossil spines. © 2015 The Linnean Society of London 相似文献
86.
Dan Swartling Mike Fry Matt Morgan Ed Biehl Jan Balzarini Erik De Clercq 《Nucleosides, nucleotides & nucleic acids》2013,32(9):2013-2019
Abstract Adducts of 3′-amino-2′,3′-dideoxythymidine and various methoxy-substituted 10-cyano-9-isothiocyanatoanthracenes were prepared for use as fluorescent-tagged molecular probes. The thymidine/anthracene adducts were subjected to antiviral assays to determine if the adducts possessed antiviral activity. 相似文献
87.
88.
Nang Thu Thu Kyaw Anthony D. Harries Palanivel Chinnakali Annick Antierens Kyi Pyar Soe Mike Woodman Mrinalini Das Sharmila Shetty Moe Khine Lwin Zuu Pyae Sone Htwe Marcelo Fernandez 《PloS one》2015,10(8)
Background
Since 2004, Médecins Sans Frontières-Switzerland has provided treatment and care for people living with HIV in Dawei, Myanmar. Renal function is routinely monitored in patients on tenofovir (TDF)-based antiretroviral treatment (ART), and this provides an opportunity to measure incidence and risk factors for renal dysfunction.Methods
We used routinely collected program data on all patients aged ≥15 years starting first-line TDF-based ART between January 2012 and December 2013. Creatinine clearance (CrCl) was assessed at base line and six-monthly, with renal dysfunction defined as CrCl < 50ml/min/1.73m2. We calculated incidence of renal dysfunction and used Cox regression analysis to identify associated risk factors.Results
There were 1391 patients, of whom 1372 had normal renal function at baseline. Of these, 86 (6.3%) developed renal dysfunction during a median time of follow-up 1.14 years with an incidence rate of 5.4 per 100 person-years: 78 had CrCl between 30–50ml/min/1.73m2 and were maintained on TDF–based ART, but 5 were changed to another regimen: 4 because of CrCl <30ml/min/1.73m2. Risk factors for renal dysfunction included age ≥45 years, diagnosed diabetes, underlying renal disease, underweight and CD4 count <200cells/mm3. There were 19 patients with baseline renal dysfunction and all continued on TDF-based ART: CrCl stayed between 30–49 ml/min/1.73m2 in five patients while the remainder regained normal renal function.Conclusions
In a resource-poor country like Myanmar, the low incidence of renal toxicity in our patient cohort suggests that routine assessment of CrCl may not be needed and could be targeted to high risk groups if resources permit. 相似文献89.
Michael J. Lawes Diana O. Fisher Chris N. Johnson Simon P. Blomberg Anke S. K. Frank Susanne A. Fritz Hamish McCallum Jeremy VanDerWal Brett N. Abbott Sarah Legge Mike Letnic Colette R. Thomas Nikki Thurgate Alaric Fisher Iain J. Gordon Alex Kutt 《PloS one》2015,10(6)
Australia has experienced dramatic declines and extinctions of its native rodent species over the last 200 years, particularly in southern Australia. In the tropical savanna of northern Australia significant declines have occurred only in recent decades. The later onset of these declines suggests that the causes may differ from earlier declines in the south. We examine potential regional effects (northern versus southern Australia) on biological and ecological correlates of range decline in Australian rodents. We demonstrate that rodent declines have been greater in the south than in the tropical north, are strongly influenced by phylogeny, and are consistently greater for species inhabiting relatively open or sparsely vegetated habitat. Unlike in marsupials, where some species have much larger body size than rodents, body mass was not an important predictor of decline in rodents. All Australian rodent species are within the prey-size range of cats (throughout the continent) and red foxes (in the south). Contrary to the hypothesis that mammal declines are related directly to ecosystem productivity (annual rainfall), our results are consistent with the hypothesis that disturbances such as fire and grazing, which occur in non-rainforest habitats and remove cover used by rodents for shelter, nesting and foraging, increase predation risk. We agree with calls to introduce conservation management that limits the size and intensity of fires, increases fire patchiness and reduces grazing impacts at ecological scales appropriate for rodents. Controlling feral predators, even creating predator-free reserves in relatively sparsely-vegetated habitats, is urgently required to ensure the survival of rodent species, particularly in northern Australia where declines are not yet as severe as those in the south. 相似文献
90.
Simon S. Jameson James Mason Paul N. Baker Paul J. Gregg David J. Deehan Mike R. Reed 《PloS one》2015,10(11)